1. Field of the Invention
The present invention relates to a method of regulating the vacuum level in a milking apparatus comprising a vacuum pump, a milking device having at least one milking means to be attached to an animal to be milked, and a conduit for the transport of a flow of air and connecting the milking device to a suction side of the vacuum pump. Moreover, the invention relates to a milking apparatus, comprising a vacuum pump, a milking device having at least one milking means provided to be attached to an animal to be milked, and a conduit connecting the milking device to a suction side of the vacuum pump and being adapted to transport a flow of air from the milking device.
2. Description of the Prior Art
Regarding vacuum pumps, there are two predominant main types. The first type comprises deplacement pumps functioning by successively forming delimited gas volumes and transporting these under pressure increase through the pump. The second main type comprises dynamic pumps in which a gas is accelerated, whereafter the kinetic energy of the gas is transformed to pressure.
Conventionally, deplacement pumps are used in milking apparatuses as vacuum pumps to produce a vacuum in a vacuum conduit connected to conduits for transporting the milk. The milk is sucked from the cows being milked via these transport conduits to a milk receiving vessel. With regard to the comfort and the udder health of the cows, it is important that the vacuum level at the teats of the cow is maintained at a relatively constant predetermined desired value. This vacuum level is dependent on the vacuum level of the vacuum conduit and thus it is also important that the latter vacuum level (the vacuum level of the milking system) is as constant as possible. Because of this, the deplacement pump is dimensioned to have a certain over-capacity in order to enable compensation for leakage in the milking apparatus or for a sudden air flow through the conduit system, for example due to the fact that a teatcup has been released from its teat, and thus the vacuum level does not decrease but remain relatively constant at the desired value. This means that during normal milking only about 50% of the capacity of the deplacement pump is utilized whereas 100% of the effect of the pump is utilized in order to provide sufficient reserve for the milking apparatus. The desired vacuum level, normally about 50 kPa, is maintained by means of a vacuum regulator letting in an appropriate air flow in the vacuum conduit. A disadvantage of this conventional way of regulating the vacuum level is that the deplacement pump normally consumes more energy than necessary since it always runs at full effect.
Moreover, it is not appropriate to regulate the vacuum level by controlling the rotational speed of a deplacement pump and in this manner obtain a lower energy consumption, since such a control is too slow and would result in unacceptable vacuum fluctuations.